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Exploring the tradeoffs between spatial resolution and q-space sampling for brain mapping with diffusion tractography: Time well spent?
Evan Calabrese1,2, Alexandra Badea1, Christopher L. Coe3, Gabrielle R. Lubach3, Martin A. Styner4,5, G. Allan Johnson1,2
1 Radiology, Center for In Vivo Microscopy, Duke University Medical Center
2 Biomedical Engineering, Duke University
3 Harlow Center for Biological Psychology, University of Wisconsin, Madison
4 Dept of Computer Science, University of NC-Chapel Hill
5 Dept of Psychiatry, University of NC-Chapel Hill
Human Brain Mapping [Article first published online: 5 JUL 2014] DOI: 10.1002/hbm.22578
Interest in mapping white matter pathways in the brain has peaked with the recognition that altered brain connectivity may contribute to a variety of neurologic and psychiatric diseases. Diffusion tractography is emerging as a popular method for brain mapping initiatives, like the human connectome project, yet it remains unclear to what extent computer generated tracks represent actual underlying anatomy. Of particular concern is the fact that diffusion tractography results can vary widely depending on the choice of acquisition protocol. The two major acquisition variables that consume scan time, spatial resolution and diffusion sampling, can each have profound effects on the resulting tractography. In this study we explore the effects of the temporal tradeoff between spatial resolution and diffusion sampling on tractography in the rhesus macaque brain, a close model of the human brain. We use the wealth of autoradiography-based connectivity data available in the rhesus macaque brain to assess the anatomic accuracy of six time-matched diffusion acquisition protocols with varying balance between spatial and diffusion sampling. We show that tractography results can vary greatly even when the subject and the total acquisition time are held constant. Further, we show that focusing on either spatial resolution or diffusion sampling at the expense of the other is counterproductive, and that a balance between the two produces the most anatomically accurate and consistent results.
Figure 1: Visualization of spatial sampling and q-space sampling in each of the six time-matched diffusion MRI protocols used in this study. For each protocol, the left half of a single coronal slice from the b0 image is shown along with a diagram of the q-space sampling scheme. The color (see legend) and radius of each q-space diagram indicates b-value, and each point represents a single measurement in q-space.
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This research was supported in part by NIH awards (R01 MH091645, P41 EB015897). We gratefully acknowledge the Wisconsin National Primate Research Center (WNPRC) for providing the specimens used in these analyses. Pathology and tissue distribution services at the WNPRC are supported by RR000167 from the NCRR and ORIP. We are grateful to Sally Gewalt and James Cook for assistance with the imaging pipelines and Gary Cofer for assistance in specimen preparation and scanning.